[RFC][PATCH] drm: kirin: Add a mutex to avoid fb initialization race

From: John Stultz
Date: Wed Feb 22 2017 - 19:57:03 EST

In some cases I've been seeing a race where two framebuffers
would be initialized, as kirin_fbdev_output_poll_changed()
might get called quickly in succession, resulting in the fb
initialization happening twice. This could cause the system
to boot up with a blank screen.

This patch adds a simple mutex to serialize it and seems to
avoid the race.

Obviously I suspect this patch isn't the best solution, but
I wanted to send it out as something concrete to discuss the

Suggestions or feedback for a better solution would be greatly

Cc: Xinliang Liu <z.liuxinliang@xxxxxxxxxxxxx>
Cc: Rongrong Zou <zourongrong@xxxxxxxxx>
Cc: Xinwei Kong <kong.kongxinwei@xxxxxxxxxxxxx>
Cc: Chen Feng <puck.chen@xxxxxxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
index ebd5f4f..80c607f 100644
--- a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
+++ b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
@@ -50,11 +50,13 @@ static int kirin_drm_kms_cleanup(struct drm_device *dev)
return 0;

+static DEFINE_MUTEX(fb_lock);
static void kirin_fbdev_output_poll_changed(struct drm_device *dev)
struct kirin_drm_private *priv = dev->dev_private;

+ mutex_lock(&fb_lock);
if (priv->fbdev) {
} else {
@@ -64,6 +66,7 @@ static void kirin_fbdev_output_poll_changed(struct drm_device *dev)
if (IS_ERR(priv->fbdev))
priv->fbdev = NULL;
+ mutex_unlock(&fb_lock);